1. Field of the Invention
The present invention relates to an apparatus and a method for plasma processing and more particularly to an apparatus and a method for plasma processing which can reduce charging damage to objects to be processed being plasma processed using the plasma processing apparatus such as a parallel plate plasma processing apparatus.
2. Description of the Related Art
For example, conventionally known techniques of this type are disclosed in Japanese Patent Laid-Open Publication No. Hei 7-201496 (Claims 3 and 9, and Paragraphs [0010], [0031], and [0037]), Japanese Patent Laid-Open Publication No. Sho 61-265820 (Claim 1, Lines 6 to 13 on the top right column on page 2, Line 5 on the top left column on page 3 to line 2 on the bottom left column on the same page, and the column stating the Effects of the Invention), and Japanese Patent No. 3113786 (Claims 1 and 2, and Paragraphs [0029] and [0030]) (hereinafter, referred to as references 1 to 3, respectively).
The reference 1 suggests an apparatus and a method for generating plasma. This apparatus includes a voltage application electrode for being applied high-frequency power, a ground electrode, and a distance adjusting mechanism for variably adjusting the distance between these electrodes. When a voltage is applied to the voltage application electrode, the distance between the voltage application electrode and the ground electrode is reduced to such an extent as to readily provide an igniting in accordance with the Paschen's law. After plasma has been produced, the distance between these electrodes is then increased, thereby ensuring a high etching capability and low damage to the processed body at the same time.
On the other hand, since the distance control mechanism for adjusting the distance between the upper and lower electrodes makes the apparatus complicated, the reference 2 suggests a plasma processing apparatus that requires no distance control mechanism. This plasma processing apparatus has two electrodes, which are isolated from each other and each connected with an individual high-frequency power supply, and the distances between these electrodes and a ground electrode disposed to face these electrodes are different. With this apparatus, the high-frequency power applied to an electrode spaced apart farther from the ground electrode is stopped immediately after a discharge is initiated, thereby allowing for readily initiating a discharge at a low voltage even for high-rate etching. In other words, different electrodes are used for plasma igniting and plasma processing.
On the other hand, the reference 3 suggests a plasma processing apparatus with a two-frequency application scheme to apply respective high-frequency powers to the upper and lower electrodes. With this apparatus, the ON or OFF timing of the high-frequency powers applied to both the upper and lower electrodes is controlled to alleviate charging damage.
However, in the conventional plasma processing methods as suggested in the references 1 and 2, the distance between the upper and lower electrodes was optimized each at the time of plasma igniting and during plasma processing to alleviate charging damage and optimize the plasma processing at the same time. However, significant progress was made since then toward finer-line and thinner-film processes for semiconductor devices followed by significant improvements in plasma processing apparatuses. This resulted in only the distance between the electrodes being optimized each at the time of plasma igniting and during plasma processing, yet causing a limitation to the prevention of charging damage.
The present invention was developed to solve the aforementioned problem. It is therefore an object of the invention to provide an apparatus and a method for plasma processing which can prevent charging damage to objects to be processed even when progress will be made toward finer-line and thinner-film processes for semiconductor devices.